Collapse process

Cavitation has three negative side effects in valves—noise and vibration, material removal, and reduced flow. The bubble-collapse process is a violent asymmetrical implosion that forms a high-speed microjet and induces pressure waves in the fluid. This hydrodynamic noise and the mechanical vibration that it can produce are far stronger than other noise-generation sources in liquid flows. If implosions occur adjacent to a solid component, minute pieces of material can be removed, which, over time, will leave a rough, cinderlike surface. 

Figure 44. Modelling the three-stage bed collapsing process. (Yang, Tung, and Kwauk, 1985.)...

Mathematical modeling of the three-stage bed collapsing process led to a more quantitative characterization of powders, in the form of a dimensionless number called th e dimens ionless subsidence time ... 

Anon, "Military Explosives , TM 9-1910 (1955), 77-85 (Munroe effect) 43) PATR 2145(1955), p Rus 15 (Russian shaped charge projectiles of WWH) 44) L.S. Holloway, Flash Radiographs Showing the Collapse Process of Copper Shaped Charge Liners , BRL Rept No 941 (1955) 45) A.M. 

Results of mathematical modeling of the bed collapsing process follow. 

This dimensionless number, designated as the dimensionless subsidence time of a power, portrays its dynamic behavior in relation to the overall bed collapsing process, inclusive of the significant variables Zn and tc. 

The carriage is provided with a slide rheostat which sends out a voltage proportional to the position of the carriage, to an xy-recorder which traces the subsidence curved simultaneously with the bed collapsing process. This same voltage is also fed to a microcomputer for data acquisition and on-line analysis. 

To make furtlicr iinprovcmcm, Tang s group is now working on the development of a 3D DM method, in which the pore collapse process is considcred. Al the same time, a new region metliod is suggested to replace the previous window method to reduce requirements for CPU time and RAM. [21]. 

The relatively mild growth and the violent collapse processes predicted by the asymptotic forms (4-210) and (4-211) are characteristic of the dynamics obtained by more general numerical studies of the Rayleigh-Plesset equation, but additional results for cases of large volume change are not possible by analytic solution. In the remainder of this section, we consider additional results that can be obtained by asymptotic methods. 

Fig. 17. Hydrodynamic and viscoplastic models for pore collapse, (a) Hydrodynamic collapse is much faster. Heat is generated when the upstream surface impacts the downstream surface. A pressure spike is generated by hydrodynamic focusing, (b) Viscoplastic collapse occurs more slowly, behind shock front. Heat is generated by viscoplastic work. Both collapse processes break up and attenuate the shock front, and generate time-delayed shocklets. Reproduced from ref. [120].

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